An in-line type pressure sensor having a structure in which a body provided with a flow channel for circulating a liquid, such as a drug solution, and a sensor body for detecting a pressure of the liquid transmitted to a pressure receiving surface through a protective sheet are integrally formed has been conventionally known (for example, see Japanese Unexamined Patent Application, Publication No. 2005-207946 (hereinafter referred to as “JP 2005-207946”)).
The pressure sensor disclosed in JP 2005-207946 detects the pressure of the fluid transmitted to the sensor body through the protective sheet mounted to a lower surface of the sensor body.